Surface changes on acetylation and exposure to ultraviolet radiation of Pinus radiata using X-ray photo-electron spectroscopy

Various Pinus radiata wood components, solvent extracted and acetylated, were irradiated with ultraviolet light (lambda(max) = 350nm). The XPS spectrum of the acetylated wood surface resembled that of cellulose acetate suggesting that acetylation removes lignin fi om the wood surface. The presence of acetylated lignin in the acetic anhydride solution following acetylation, identified by IR and NMR, supports this theory. This could be a major contributor to the bleaching of wood on acetylation. The XPS spectra of irradiated wood and lignin showed that photo-oxidation had occurred in both extracted wood, untreated lignin and acetylated samples. Demethoxylation and/or beta-aryl ether cleavage in untreated irradiated lignin is supported by the XPS Spectra while deacetylation of irradiated acetylated samples is indicated by decreased C-1 band intensity. Acetylation proved ineffective in preventing photo-oxidation of wooden surfaces. The depletion of lignin on the wooden surface, (an artefact of acetylation) results in less light absorption thereby retarding photo-induced yellowing. Peroxide treatment of extracted radiata pine did not deplete surface lignin.